Method of constructing stationary induction apparatus



y 8, 1962 A. G. STEINMAYER ET AL 3,032,863

METHOD OF CONSTRUCTING STATIONARY INDUCTION APPARATUS 2 Sheets-Sheet 1 Filed July 22, 1955 INVENTORS 141001111. 5'- Slain-"payer James G. Everharl .l llornely y 8, 1962 A. G. STEINMAYER ETAL 3,032,863

METHOD OF CONSTRUCTING STATIONARY INDUCTION APPARATUS Filed July 22, 1955 2 Sheets-Sheet 2 kw Y 1 fl INVENTORS' fllnrin G- teinma yer ames G. Ever-ha! United States Patent METHOD OF CONSTRUCTING STATIONARY INDUCTION APPARATUS Alwin G. Steinmayer, Milwaukee, Wis., and James G. Everhart, Sherman, Tex., assignors to McGraw-Edison Company,a corporation of Delaware Filed July 22, 1955, Ser. No. 523,750 4 Claims. (Cl. 29-15557) This invention relates to a method of constructing stationary induction apparatus and in particular to a method of constructing magnetic cores for electrical transformers.

The present application is a continuation-in-part of our United States application Serial No. 262,622 filed December 20, 1951, now abandoned, and having the same assignee as the present invention.

A magnetic core constructed by spirally winding continuous magnetic ribbon flatwise into a closed loop in accordance with the method disclosed in U.S. Patent 2,288,855 to Steinmayer et al., having the same assignee as the subject invention, is generally considered to be an ideal transformer core. Such a wound core provides a continuous flux path with a minimum number of airv gaps which results in uniformly low exciting current. The laminations minimize eddy current losses, and the round shape of the electrical windings provides low impedance and great short circuit strength.

Continuous strip cold rolled silicon steel having crystal lattices arranged with their axes of easiest magnetization lengthwise of the strip is an excellent material for such a core. However, continuous strip oriented silicon steel is difiicult to manufacture and often more difiicult to procure. In fact, at times when vital materials have been assigned to urgent defense needs it has been impossible to purchase such steel for transformer manufacture. The method of magnetic core construction of the present invention permits the utilization of oriented magnetic material in sheet form which is more readily available than continuous strip magnetic material. I

It is an object of the invention to provide a method of constructing a wound magnetic core from laminations cut from magnetic material in sheet form.

Wound cores are known comprising concentrically nested, flatwise curved laminations wound flatwise consecutively end to end which can be assembled to and disassembled from a preformed winding and wherein butt joints occur between successive laminations. In the conventional method of constructing such a core, continuous magnetic'strip material is spirally wound, shaped to the contour of the finished core, annealed in such shape to permanently set the magnetic strip material, and then cut to predetermined lamination lengths which are inserted through the window of an electrical winding. In addi tion to the disadvantage that this prior art method necessitates continuous strip magnetic material, the cutting of the magnetic material after annealing deleteriously affects the crystalline structure and introduces appreciable strains in the magnetic steel.

It is a further object of one embodiment of the invention to provide a method of constructing a wound core from laminations which can be cut from magnetic material in sheet form and assembled to and disassembled from an electrical winding wherein the cutting of thelaminations to desired length is accomplished prior to annealing, and consequently, no deleterious strains due to cutting occur in the magnetic material.

In magnetic cores having butt joints between successive laminations, the magnitude of the exciting current increases with the air gap spacing between adjoining ends of successive laminations, and in prior art cores, no means were provided to prevent change of this spacing in the finished core.

3,032,863 Patented May 8, 1962 It is a still further object of the invention to provide a method of constructing a wound core of concentrically nested, flatwise curved end-to-end laminations which provides a minimum spacing between the adjoining ends of successive laminations.

Another object of one embodiment of the invention is to provide a method of constructing a wound core of concentrically nested, flatwise curved, laminations wound flatwise consecutively end to end in convoluted layers which can be assembled to and disassembled from a preformed electrical winding and which assures that the spacing between adjoining ends of successive laminations is a minimum in the finished core. An object of an alternative mode of practicing the invention is to provide a method of constructing such a magnetic core wherein laminations which can be assembled to and disassembled from an electrical winding are formed to permit interlocking the ends of successive laminations.

For a better understanding of the principles and advantages of the method of the invention, reference should be had to the following detailed description and the accompanying drawing wherein:

FIG. 1 illustrates the spiral Winding of laminations cut from sheet magnetic material, successively flatwise in end to end relationship in convoluted layers and the securing of adjoining ends of successive laminations together during the winding to form a closed core;

FIG. 2 illustrates that the means utilized for securing the adjoining ends of successive laminations in the closed core shown in FIG. 1 disintegrate during annealing;

. FIG. 3 is a perspective view of a transformer incorporating magnetic cores constructed in accordance with the method of the invention;

FIGS. 4 through 6 illustrates an alternative mode of practicing the invention by peripherally staggering the butt joints in adjoining layers and tack welding the ends of each lamination to the magnetic steel of an adjoining layer. In the embodiment of the method illustrated in FIGS. 4 and 5, a continuous strip including two superimposed layers, each having laminations end to end in substantially abutting relation is spirally wound flatwise, whereas in the embodiment illustrated in FIG. 6 single laminations are spirally and flatwise wound successively in end to end relationship in convoluted layers and the end of each lamination is tack welded to the convolution radially inward therefrom;

FIG. 7 illustrates still another mode of practicing the method of the invention including the steps of forming each lamination with a female element at one end and a male element at the opposite end complementary to the female element to permit interlocking successive laminations;

FIG. 8 illustrates the step of securing the adjoining ends of successive laminations having a diagonal butt joint therebetween; and

FIG. 9 illustrates still another mode of practicing the invention including the steps of spirally winding laminations successively flatwise in convoluted layers and affixing the terminating end of one lamination and the starting end of the succeeding lamination to an adjoining convolution by adhesive to hold the adjoining ends of successive laminations in substantially abutting relation.

The method of the present invention utilizes many of the steps of the well known method of constructing a wound strip core disclosed in the aforementioned United States Patent 2,288,855 to Steinmayer et al., one of the patentees being a coinventor of the subject invention. In this prior art method continuous magnetic ribbon is spirally wound on a mandrel to form a closed core, the closed core is shaped to desired configuration, and the core so shaped is annealed to relieve internal strains in the magnetic material and to permanently set the magnetic ribbon.

A magnetic core constructed in accordance with this prior art method is generally considered ideal for electrical transformers in that a minimum number of air gaps occur and consequently, the exciting current is a minimum.

The method of the present invention permits the construction of a magnetic core only slightly inferior magnetically to such a wound strip core from laminations cut from magnetic material in sheet form so that the direction of easiest magnetization is lengthwise thereof. Further, certain embodiments of the method of the invention permit assembling and disassembling of the laminations to a preformed electrical winding.

In a magnetic core having butt joints between adjoining ends of successive laminations, the magnitude of the exciting current increases with the spacing between said adjoining ends, i.e., with air gap spacing. Consequently, it is desirable in the present method of constructing a wound core of concentrically nested, fiatwise curved convolutions from laminations cut from oriented magnetic steel in sheet form, that the adjoining ends of successive laminations abut in such manner that air gap spacing is a minimum.

FIG. 1 illustrates one method of spirally winding a plurality of laminations, cut from oriented magnetic steel in sheet form so that the direction of easiest magnetization is lengthwise thereof, successively flatwise in end to end relationship in convoluted layers and securing adjacent ends of successive laminations tightly together at 2 during the winding by adhering means such as heat-disintegratable gummed paper, or pressure sensitive, tape 3. For purposes of illustration, the thickness of the adhering means must necessarily be exaggerated in FIG. 1, but in reality it is so thin that it has substantially no effect in causing bulges in the finished core. The tape 3 is affixed along the flat surfaces of two successive laminations, holding adjoining ends thereof in such close proximity that a minimum air gap exists therebetween. The ends of the outermost lamination are secured in overlapping relation by tape 3 to prevent unwinding of the laminations. As disclosed in the aforementioned Patent 2,288,855, the spiral winding may be directly on a mandrel having a contour corresponding to the window of the finished core, e.g., a rectangular mandrel to form the closed core illustrated in FIGS. 1-3, or the spiral and flatwise winding of the successive laminations with adjoining edges secured together by tape 3 may be on a circular mandrel to form a closed hollow core of annular configuration'as illustrated in FIGS. 5 and 6 which is subsequently shaped to the desired contour. The core so shaped is then strain relief annealed to remove internal strains due to the work ing of the metal in the Winding and shaping steps and to permanently set the laminations in desired configuration. 1

FIG. 2 illustrates the core of FIG. 1 after the annealing step and shows that during the annealing the heat-disintegratable pressure sensitive tape burns away leaving a well integrated core with a substantially continuous path 'for the flow of magnetic flux. It Will be appreciated that during annealing the laminations assume a permanent set so that after annealing the adjoining ends of successive laminations are in the same abutting relation that they were held by the tape 3 before the tape disintegrated.

Although an electrical winding may be wound about the winding legs of closed magnetic cores made in accordance with the method of the invention to construct the transformer illustrated in FIG. 3, it will be appreciated that the permanently set laminations can be inserted vention are lower than those of cores manufactured in accordance with prior art methods wherein continuous magnetic strip is spirally wound, annealed, and then cut to predetermined lengths to permit threading the cut lengths through a preformed winding, and such cutting after annealing deleteriously affects the crystalline structure of the magnetic material.

FIGS. 4-6 illustrate an alternative mode of practicing the invention wherein the adjoining ends of successive, concentrically nested laminations wound flatwise end to end in convoluted turns are held in butt-jointed relation by staggering the butt joints in adjoining layers and tack welding, or spot welding, the ends of each lamination to the metal in an adjoining layer. In the embodiment illustrated in FIGS. 4 and 5 a continuous strip including two superimposed, magnetic material lamination thicknesses are simultaneously spirally wound flatwise into convoluted layers, whereas in the mode of practicing the invention illustrated in FIG. 6 each spiral convolution is only a single lamination thick. Welding the adjoining ends of peripherally successive laminations directly in abutting relation would deleteriously affect the crystalline structure of the magnetic steel, and it will be appreciated that the tack welding occurs between the end of the lamination and the steel of the adjacent lamination layer, and inasmuch as the tack welding is only at the edges of the strip,

the deleterious strains introduced by the tack welding are not appreciable.

In the species of the method illustrated in FIGS. 4 and 5, laminations cut from magnetic steel sheet to have a preferred grain orientation lengthwise thereof are used to produce the equivalent of a continuous strip by superimposing laminations in two layers each including a plurality of laminations in end-to-end butt-jointed relationship and staggered relative to the butt joints in an adjacent layer, and tack welding the ends of each lamination to the lamination of the adjoining layer. The continuous magnetic material structure effected in the manner illustrated in FIG. 4 is spirally wound flatwise as shown in FIG. 5 into convolutions which are two laminations thick.

In the mode of practicing the invention illustrated in FIG. 6 the lamination lengths are spirally wound successively flatwise with a single lamination thickness in each convolution and the tack welding is performed during the winding operation and is always to the magnetic material of the radially inward convolution. FIGS.

5 and 6 illustrate the spiral and flatwise winding to cir- V is annealed subsequent to the winding and shaping operations to remove strains in the magnetic material.

It will be appreciated that the laminations cannot be disassembled from a core constructed in accordance with the mode of practicing the invention illustrated in FIGS. 4-6 and that the electrical coil must be wound around a winding leg of such a magnetic core.

FIG. 7 illustrates a mode of practicing the method of the invention wherein the laminations are formed with a female element on one end and a male element on the opposite end thereof complementary to said female element to; permit interlocking the ends of successive laminations. It will be appreciated'that the spacing between adjoining ends of successive laminations in a core constructed in accordance with this species of the invention will not only be a minimum but will be mechanically held to prevent an increase inthe air gap spacing. One end 10 of each lamination is formed with a flaring tongue 11 that increases in width toward its end 1111 and the opposite end 12 of each lamination strip is formed with a flaring recess complementary to the tongue 11 thereby permitting the adjoining ends of successive laminations to be dovetailed together. If desired, the adjoining ends and 12 of successive laminations may be connected by pressure sensitive tape as in the method illustrated in FIG. 1. It will be appreciated that the laminations of a core constructed in accordance with this embodiment of the invention can be assembled to a preformed electrical winding and the ends of successive laminations interlocked after insertion through the window of the winding.

FIG. 8 shows that the method illustrated in FIG. 1 can be utilized to secure the adjoining, diagonally cut ends 13 of successive laminations 14 and 15 together by applying a strip of adhesive material 16 along the flat surfaces of the two successive laminations to hold the adjoining diagonally cut ends 13 with a minimum air gap therebetween.

In the embodiment of the invention illustrated in FIG. 9, laminations cut from magnetic steel in sheet form are spirally and flatwise wound successively in end to end relation in convoluted layers and a suitable adhesive 17 is applied to the radially inward convoluted layer at the terminating end 18 of each lamination. The terminating end 18 of the lamination is pressed against the adhesive 17 and the starting end of the succeeding lamination (not shown) is likewise pressed against the adhesive 17 to hold the adjoining ends of successive laminations in substantially abutting relation.

While we have disclosed several alternative modes of practicing the method of the invention, it will be appreciated they are illustrative only and that changes and modifications therein will be apparent to the man skilled in the art, and it is intended in the appended claims to cover all such changes and modifications as come within the true spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. The method of constructing a wound, closed magnetic core of concentrically nested, flatwise curved, convolutions of magnetic material, said method including the steps of providing a plurality of elongated, straight laminations of magnetic material each having a preferred grain orientation lengthwise thereof, forming said laminations with interlocking means on opposite ends thereof one of which is a male element and the other of which is a female element complementary to said male element, spirally winding said laminations successively flatwise in end to end relation in convoluted layers closely adjacent each other along substantially their entire length to form a closed magnetic core and engaging said male and female elements of successive laminations during the winding to interlock said successive laminations, strain relief annealing said closed core to pre-set said laminations in the configuration of said closed core, disassembling said laminations, and reassembling said laminations through the window of an electrical winding in the same relative positions they occupied during annealing.

2. The method of constructing stationary induction apparatus, comprising the steps of providing a plurality of elongated, straight laminations of magnetic material each having a preferred grain orientation lengthwise thereof, winding and shaping said laminations flatwise successively in convoluted layers closely adjacent each other along substantially their entire length and securing the ends of successive laminations in substantially abutting air gap relation during the winding operation to form a closed approximately rectangular magnetic core, strain relief annealing said closed core to give said laminations a permanent set of approximately rectangular configuration, disassembling said laminations from said closed core and applying said laminations successively, beginning with the innermost lamination, to the winding leg of a preformed electrical winding by inserting said permanently set laminations through a window of said electrical winding and concentrically stacking the laminations consecutively in end to end relation in convoluted turns embracing said winding leg with the laminations occupying the same relative position which they had during the annealing.

3. The method of constructing stationary induction apparatus, comprising the steps of providing a plurality of elongated, straight laminations of magnetic material each having a preferred grain orientation lengthwise thereof, forming said laminations with interlocking means on opposite ends thereof one of which is a male element and the other of which is a female element complementary to said male element, spirally winding said laminations consecutively in convoluted layers closely adjacent each other along substantially their entire length to form a closed magnetic core and engaging said male and female elements of successive laminations during the winding to interlock said successive laminations, strain relief annealing said closed core to give said laminations a permanent set, separating said laminations from said core, and linking said laminations to the winding leg of a preformed electrical winding by threading the laminations successively, beginning with the innermost lamination, through the window of said electrical winding and con centrically stacking the laminations consecutively in end to end relation in convoluted turns with the male and female elements of successive laminations in engagement and with the laminations occupying the same relative position which they had during the annealing.

4. The method of constructing a wound, closed magnetic core of concentrically nested, flatwise curved convolutions of magnetic material, said method including the steps of providing a plurality of elongated laminations of magnetic material each having a preferred grain orientation lengthwise thereof, flatwise winding said laminations successively in convoluted layers lying closely adjacent each other along substantially their entire length and releasably securing adjacent ends of successive laminations in substantially abutting relation during the winding and shaping said laminations to form a closed, approximately rectangular magnetic core, strain relief annealing said core while so shaped to pre-set said laminations in approximately rectangular configuration, disassembling said laminations, and reassembling said pre-set laminations through the window of an electrical Winding in the same relative positions they occupied during annealing.

References Cited in the file of this patent UNITED STATES PATENTS 1,857,215 Ruder May 10, 1932 1,935,426 Acly Nov. 14, 1933 2,305,649 Vienneau Dec. 22., 1942 2,313,306 Wiegand Mar. 9, 1943 2,477,350 Somerville July 26, 1949 2,595,820 Somerville May 6, 1952 

